Holography, also known as gauge-gravity duality or the AdS/CFT correspondence, is an extremely useful tool for studying systems involving strongly-coupled degrees of freedom. Although the systems we study in holography do not describe the real world, they have the potential to reveal general principles applicable to real systems. Indeed, holography revealed that the low ratio of shear viscosity to entropy density in the quark-gluon plasma is in fact generic to strongly-coupled plasmas. In this talk I will describe a holographic calculation of another transport coefficient, a conductivity, associated with flavor fields (quarks) in a strongly-coupled plasma. The result reveals how holography captures a lot of real-world physics, such as momentum dissipation and Schwinger pair production, and moreover provides hints of universality in the charge transport of strongly-coupled systems.